PubMed Health⌕ Search

Biomedical subjects

M L Sotgiu

Publications and source records attributed to M L Sotgiu.

At least 55 records · Page 3Linked to original sources
PubMed1987

The effects of periaqueductal gray and nucleus raphe magnus stimulation on the spontaneous and noxious-evoked activity of lateral reticular nucleus neurons in rabbits.

In urethane-anesthetized rabbits the effects of periaqueductal gray (PAG) and nucleus raphe magnus (NRM) stimulation on the spontaneous and noxious-evoked activity of the lateral reticular nucleus (LRN) neurons were studied. The PAG and the NRM stimulating electrodes were located in the optimal sites for suppressing the jaw-opening reflex (JOR) evoked by the tooth pulp stimulation. It was found that the 12% of neurons tested were affected by one or both stimuli. A total of 80 responsive neurons (52% antidromically activated by the cerebellum) were analyzed. Out of these neurons, 31 showed a convergence to both stimuli, 43 responded only to PAG and 6 only to NRM. Noxious heat stimulation of the contralateral foot was effective in altering the activity of 60% of these neurons. The PAG and NRM stimuli modified the noxious-evoked responses in most of these units. While the excitation was the predominant effect on the spontaneous activity (52 cells), the inhibition was predominant on the noxious-evoked activity (29 cells). These results indicate the presence of connections from PAG and NRM to LRN, probably devoted to the processing of the nociceptive information.

Action Potentials↗
PubMed1987

Projections from lateral reticular nucleus neurons to trigeminal motor nucleus revealed by antidromic activation in rabbits.

In anesthetized rabbits, electrophysiological experiments were conducted to determine if neurons of the lateral reticular nucleus that modified their activity during masticatory movements project directly into the trigeminal motor nucleus. Of the 125 neurons tested, 50 responded to stimulation of the trigeminal motor nucleus; of these, 22 were antidromically excited. Among this last population, 9 were antidromically driven also by cerebellar stimulation. In these neurons the antidromic response evoked from one structure collided with the response antidromically evoked from the other, thus indicating that both potentials are from the same neuron projecting to the trigeminal motor nucleus and the cerebellum. The remaining 28 neurons responding to stimulation of the trigeminal motor nucleus were orthodromically activated with a wider range of latencies. The possible significance of these findings in the organization of the rhythmic masticatory movements is briefly discussed.

Action Potentials↗
PubMed1986

Effects of noxious stimuli on neurons of the lateral reticular nucleus region in rabbits.

The responses of neurons in the lateral reticular nucleus region (LRN) to both noxious spinal (radiant heat) and trigeminal inputs (tooth pulp stimulation), were analyzed in 12 anesthetized and paralyzed rabbits. It was found that 20% of neurons tested were affected by one or both noxious stimuli and 58% of these cells could be antidromically activated by stimulation of the cerebellum. In the majority of cell (85% of the heat-responding, and 72% of the tooth pulp-responding) the effect of noxious stimuli was excitatory and in the remaining cells was inhibitory. Furthermore 53% of responding neurons showed a convergence to spinal and trigeminal input. The type of response was the same (excitation) in 63% of these units, but was different in the others. These data support the view of an involvement of the LRN region in the mechanisms of the nociceptive information and suggest the possibility that the cerebellum may also contribute to some aspects of these mechanisms.

Animals↗
PubMed1986

Inhibition of the nociceptive jaw opening reflex by the lateral reticular nucleus (LRN) in the rabbit.

The effect of stimulation of the lateral reticular nucleus (LRN) on the jaw opening reflex (JOR), evoked by tooth pulp or by palatal tissue stimulation, was studied in anesthetized rabbits. The results show an inhibitory effect on the JOR evoked by tooth pulp stimulation, which is considered a nociceptive reflex, while no effect is shown on the JOR evoked by palatal tissue stimulation. The maximum effect was observed at intervals of 30-50 ms between the two stimuli and the more effective site of inhibition in the nucleus was found to be the ventrolateral portion. The result of a selective effect of LRN stimulation on nociceptive reflexes supports the view of a role of this nucleus in the central mechanisms of pain control.

Animals↗
PubMed1985

Single unit activity in lateral reticular nucleus during cortically evoked masticatory movements in rabbits.

The activity pattern of the lateral reticular nucleus (LRN) neurones was analyzed during cortically evoked masticatory movements in anesthetized rabbits. Antidromic activation from the cerebellum and histological reconstruction of recorded neurones location from electrode tracks and microdrive readings were the criteria for neuronal identification. Tonic changes as well as rhythmic modulation of neuronal activity were found in a subpopulation of LRN cells during mastication. The same results were observed also in curarized rabbits during fictive mastication. These data support the view that LRN neurones are involved in a central mechanism controlling the masticatory movements.

Animals↗
PubMed1985

Response of ventrobasal thalamic neurons activated by dorsal and dorsolateral funiculi: an intracellular study.

Intracellular responses to stimulation of the dorsal column (DC) and dorsolateral funiculus (DLF) were recorded in cells of the thalamic ventrobasal complex (VB) in anesthetized cats, with the dorsal funiculi either intact or isolated. The responsiveness of VB neurons was tested using graded stimulation, paired-shock, and interaction techniques. Of the 60 VB neurons thoroughly studied, 50 responded to stimulation of the DC with excitatory postsynaptic potentials (EPSPs) followed by inhibitory postsynaptic potentials (IPSPs); half of these 50 neurons responded to stimulation of the DLF with the same pattern, whereas no IPSPs could be elicited in the remaining neurons. The majority of EPSPs could be fractionated into unitary components during graded electrical stimulation. The number of such components observed was greater after DLF than after DC stimulation. In most neurons, the DLF-evoked EPSPs were smaller in amplitude than the DC-evoked EPSPs. Paired-shock stimulation facilitated the DLF excitatory responses. The amplitude of IPSPs induced by DLF stimulation was significantly smaller than that evoked by DC stimulation, and DC stimulation reduced the excitatory response to subsequent DLF stimulation. The data support the known dominance of the DC pathway in the cat.

Animals↗
PubMed1984

A study of the relationship between muscle length, tension-time area and stiffness in cat areflexic soleus.

The relationship between muscle length and both tension-time area and stiffness were studied in the isolated cat soleus muscle during tetanic isometric contraction at different stimulus rates. The results show that: The area subtending the tension curve remains constant in a range of 8-10 mm of muscle length, for stimulation frequencies between 15 and 66 Hz. The muscle stiffness, measured using different amplitude stretches, remains constant over changes in muscle length of 10 mm. The stiffness is higher for smaller stretches than for larger ones. The data therefore show an approximately constant tension-time area and no significant changes in stiffness for variations in muscle length that exceed the physiological length variations during quiet standing. These results are discussed in the context of postural mechanisms.

Animals↗
PubMed1983

Intracellular study of presumed interneurons in the ventrobasal complex of cats with chronic cortical ablations.

In a ventrobasal neuronal population surviving chronic ablation of somatosensory and motor cortices, the input-output properties of cells activated by ML fibers and showing functional characteristics of interneurons (large peripheral receptive fields, convergence of different types of receptor afferents, repetitive discharge) were studied. Since intracellular recordings showed the presence of excitatory and inhibitory postsynaptic potentials, it is argued that inhibitory interneurons also receive inhibitory inputs, suggesting that data processing in VB is more complex than hitherto postulated.

Animals↗
PubMed1983

An HRP study in the cat of pathways which may interconnect the two ventrobasal complexes.

Possible direct or indirect connections between the two VB thalamic complexes were investigated using the HRP technique. Labelled cells were found ipsilaterally in the NCP and in NRT following injections n the VB complex and in the ipsilateral NRT and in contralateral NCP following injections in NCP. No labelling of contralateral VB complex was ever found. A pathway involving NRT and NCP is suggested to support the possibility of indirect connections between the two thalami and the functional implications of the described projections are discussed.

Animals↗
PubMed1981

A horseradish peroxidase study of afferent projections to nucleus reticularis thalami in the cat.

Afferent projections from both the reticular formation and the thalamic relay nuclei to nucleus reticularis thalami (R) were studied using the HRP technique. Injections were performed in different regions of the nucleus. Numerous labelled cells were found ipsilaterally in i) the lateral geniculate nucleus (GL) following HRP injections in dorsolateral regions of R and in ii) the ventrobasal complex (VB) following HRP injections in the ventral regions. No labelling of brain stem reticular structures was ever found. These results provide evidence for a direct projections from the VB and GL nuclei to R. The functional meaning of these data is discussed in relation with previous anatomical and neurophysiological findings. The hypothesis of a significant role of R in feedback circuits modulating sensory information seems to be supported.

Afferent Pathways↗
PubMed1979

Interactions between spinocervicolemniscal and dorsal column pathways in thalamic ventrobasal neurons in the cat.

Ventrobasal (VB) thalamic cells responding to electrical stimulation of the dorsal column (DC) and of the dorsolateral funiculus DLF in cats with DC intact or cut at C4 and isolated, were studied. Among the cells observed, about 30% showed convergence to the two pathways. Different patterns of interaction between the two inputs were found, but the most frequent effect observed was an inhibition exerted by dorsal column (conditioning) stimulation on the activity evoked by dorsolateral funiculi (test) stimulation. From these results a dominance of the DC over the spinocervico-thalamic (SCT) inputs was confirmed.

Animals↗
PubMed1976

Electrophysiological identification of pontomedullary reticular neurons directly projecting into dorsal column nuclei.

In cats 'encephale isole', cerebellectomized and curarized, neurons projecting from the bulbopontine reticular formation to the cuneate nucleus were identified by stimulating their axons in this nucleus by means of Eide micropipettes and by recording both field potential and antidromic responses from single somata in the nucleus gigantocellularis. Of 130 neurons responsive to cuneate stimulation, 17 (12%) were found that were antidromically activated. The small proportion of antidromic responses might reflect the small size of the projection pathway. However, there are reasons to believe that a certain number of neurons might have been missed because of biasing factors introduced by the microstimulation technique. Neurons that were activated orthodromically were also observed, responding after latencies spread over rather wide ranges. The possible pathways for this activation are discussed.

Animals↗